In recent years, scanning laser ophthalmoscopes (SLOs) that irradiate the fundus with laser light in two dimensions and receive reflected light therefrom and imaging apparatuses that utilize the interference of low coherence light have been developed as ophthalmic image pickup apparatuses. The imaging apparatuses utilizing the interference of low coherence light are called optical coherence tomography (OCT) systems, which are in particular used to acquire a tomogram of the fundus or the vicinity thereof. Various kinds of OCT have been developed, such as time domain OCT (TD-OCT) and spectral domain OCT (SD-OCT).
In particular, the resolution of such ophthalmic image pickup apparatuses has recently been improved by, for example, achieving high NA of irradiation laser light. However, when an image of the fundus is to be acquired, the image must be acquired through optical tissues including the cornea and the crystalline lens. As the resolution increases, the aberrations of the cornea and the crystalline lens have come to significantly affect the quality of acquired images. Thus, studies of AO-SLO and AO-OCT in which adaptive optics (AO) that is a correction optical system that measures the aberration of the eye and corrects the aberration is incorporated in their optical system have been pursued. An example of AO-OCT is shown in Y. Zhang et al, Optics Express, Vol. 14, Nos. 10 and 15, May 2006. The AO-SLO and AO-OCT generally measure the wavefront of the eye using a Shack-Hartmann wavefront sensor system. The Shack-Hartmann wavefront sensor system measures the wavefront by introducing measurement light into the eye and receiving its reflected light with a CCD camera through a microlens array. A deformable mirror or a spatial-phase modulator is driven to correct the measured wavefront, and an image of the fundus is acquired therethrough, thus allowing AO-SLO and AO-OCT to acquire a high-resolution image.
In general, achieving high NA for irradiation laser light to increase the resolution increases the amount of aberration due to the optical tissues, such as the cornea and the crystalline lens, and forms the aberration into a complicated shape. This aberration is to be corrected by AO; however, to correct a large amount of aberration or an aberration of complicated shape, it is necessary to measure the aberration at high resolution and to drive a wavefront correction device at high resolution. However, it is impossible to correct an aberration beyond the correction capacity of the wavefront correction device. Furthermore, to measure an aberration at high resolution and drive the correction device at high resolution, a large number of calculations are needed, thus posing the significant problem of an increase in calculating time. In particular, since the aberration of the eye should be repeatedly corrected at high speed because the state of tear and the state of visibility control changes constantly, an increase in processing speed is very important.